Apparatus and method for navigating vehicle to destination using display unit

ABSTRACT

A bird&#39;s eye view commonly used in a flight simulation is applicable to an apparatus and method for navigating a vehicle running on a set route of travel to a set destination using a (color) display unit according to the present invention. The bird&#39;s eye view of a road map surrounding a present position of the vehicle has a viewing point placed at a predetermined position on an upper sky in a direction opposite to the set destination with the present position of the vehicle as a reference and has a line of sight looking down over the road map so that a part of the road map surrounding the present position of the vehicle can be viewed in an extended scale form and the remaining part of the road map remote from the present position and nearer to the set destination can be viewed in a gradually reduction scale form.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to an apparatus and method for navigatinga vehicle to a destination to which a vehicle occupant desires to reachusing a display unit.

2. Description of Background Art

Various types of vehicular navigating systems (also called, vehicularroute guidance apparatuses) in which an optimum route of travel from astart point of the vehicle to a destination is searched and derived andboth of the optimum route and a present position of the vehicle aredisplayed on a display screen of a display unit have been proposed.

FIG. 1A exemplifies a displayed image in a case of one of the previouslyproposed vehicular navigating systems.

As shown in FIG. 1A, the present position of the vehicle is superimposedand displayed on the display image screen with an arrow mark and withits surrounding portion of the arrow marked present position encircledby a dotted line. Then, when an operator operates a predeterminedswitch, a range encircled with the dotted line is displayed in anextended form as shown in FIG. 1B. This permits the operator torecognize a road (traffic) situation surrounding the present position indetails. In this way, when the displayed images are exchanged from FIG.1A to FIG. 1B and vice versa, it is always necessary to operate thepredetermined switch. This makes the operation troublesome.

On the other hand, another previously proposed navigating system inwhich road maps having different reduction of scales are simultaneouslydisplayed on the display image screen, this display form being,so-called, superimposed displayed patterns, as shown in FIG. 2.

FIG. 2 exemplifies the displayed image screen of the other previouslyproposed vehicular navigating system, with intersection situationssurrounding the present position of the vehicle being displayed in theextended scale form on a right upper corner of the displayed imagescreen. This other previously proposed navigating system permits thevehicular occupant to recognize the road map having a wide range of viewwith the present position of the vehicle as a center and to recognizethe road (traffic) situation surrounding the present position of thevehicle in details.

However, since, in the displayed image screen shown in FIG. 2, the partof the road map has been displayed on the right upper corner of thedisplayed image screen in the extended scale form, the actual road mapto be displayed on the right upper corner of the displayed image screencannot be viewed from the displayed image screen (is hidden by theextended part of the road map). Hence, in a case where, for example, thevehicle driver tries to turn a right corner corresponding to thedisplayed portion of the hidden part (not displayed), the vehicle drivercannot recognize a road (traffic) situation in the forward direction.This makes the vehicle driver inconvenient.

SUMMARY OF THE INVENTION

It is, therefore, a principal object of the present invention to providean apparatus and method for navigating a vehicle with a display unitwhich can solve the above-described problems by coordinate systemtransforming a road map image data into a desired bird's eye view sothat the switch to change a reduction scale percentage of the road mapas shown in FIGS. 1A and 1B is not needed and no such a limitation ofthe displayed range as shown in FIG. 2 occurs.

According to one aspect of the present invention there is provided anapparatus for navigating a vehicle using a display unit, comprising: a)road map storing means for storing a road map data related to a roadmap; b) vehicle position detecting means for detecting a presentposition of the vehicle; c) vehicle destination setting means throughwhich a destination to which the vehicle is desired to reach is set onthe road map; d) start point setting means for setting a start point oflocation on the road map at which the vehicle is to start on the basisof the detected present position of the vehicle; e) route of travelsetting means for setting a route of travel on the road map from thestart point to the set destination; and f) display control means forcontrolling an image of the road map surrounding the set route of travelto be displayed on a display image screen of the display unit, the imageof the road map surrounding the set route of travel to be displayed onthe display unit being taken in a form of a desired bird's eye viewachieved when the bird's eye as a viewing point is placed at apredetermined position on an upper sky located in a direction oppositeto the set destination with the present position of the vehicle as areference and the road map surrounding the set route of travel beinglooked down over from the bird's eye.

According to another aspect of the present invention there is provided amethod for navigating a vehicle using a display unit, comprising thesteps of: a) storing a road map data related to a road map in apredetermined storing means; b) detecting a present position of thevehicle; c) setting a destination to which the vehicle is desired toreach is set on the road map; d) setting a start point of location onthe road map at which the vehicle is to start on the basis of thedetected present position of the vehicle; e) setting a route of travelon the road map from the start point to the set destination; and f)displaying on a display image screen of the display unit the image ofthe road map surrounding the set route of travel; and g) operativelytransforming a coordinate system of the road map surrounding the setroute of travel into a desired bird's eye view achieved when the bird'seye as a viewing point is placed on an upper sky located in a directionopposite to the set destination with the present position of the vehicleas a reference and the road map surrounding the set route of travelbeing looked down over from the bird's eye.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are explanatory views of examples of road map on adisplay image screen of a display unit in a former previously proposednavigation system described in the BACKGROUND OF THE INVENTION.

FIG. 2 is an explanatory view of another example of road mapssimultaneously displayed on the display image screen of the display unitin a latter previously proposed navigation system described in theBACKGROUND OF THE INVENTION.

FIG. 3A is a schematic explanatory view of a bird's eye view preparedfrom a viewing point for explaining the bird's eye view applicable to anapparatus and method for navigating a vehicle using a display unitaccording to the present invention.

FIG. 3B is a schematic explanatory view of a bird's eye view in athree-dimensional coordinate system with a viewing point on a Z axis.

FIG. 4 is an explanatory view of an example of a displayed image screenin which the present position of the vehicle, a set optimum route oftravel to a destination are displayed with the bird's eye view shown inFIG. 3.

FIG. 5 is a schematic circuit block diagram of the apparatus fornavigating the vehicle using the display unit in a first preferredembodiment according to the present invention.

FIG. 6 is an operational flowchart for explaining an operation of thenavigating apparatus shown in FIG. 5.

FIG. 7 is an operational flowchart for explaining a subroutine of a stepS5 in FIG. 6.

FIG. 8 is an explanatory view for explaining a displayed image on adisplay image screen in the case of the first embodiment.

FIG. 9 is an explanatory view for explaining the displaying methodexecuted in the subroutine of the step S5 in FIG. 7.

FIG. 10 is an operational flowchart of the navigating apparatus in asecond preferred embodiment according to the present invention.

FIG. 11 is an explanatory view of an example of the displayed imagescreen of the bird's eye view in the case of the second embodiment shownin FIG. 10.

FIG. 12 is an operational flowchart of a subroutine of a step S5 in FIG.6 in a case of a third preferred embodiment of the vehicular navigatingapparatus according to the present invention.

FIG. 13 is an explanatory view for explaining a positional relationshipbetween a viewing point and the present position of the vehicle in thecase of the third preferred embodiment shown in FIG. 12.

FIG. 14 is an explanatory view for explaining a relationship between adirection of a line of sight and a range of the road map displayed onthe display unit in the case of the third embodiment.

FIG. 15 is a schematic circuit block diagram of the vehicular navigatingapparatus in a case of a fourth preferred embodiment according to thepresent invention.

FIGS. 16A and 16B are integrally an operational flowchart for explainingthe operation of the navigating apparatus in the case of the fourthembodiment shown in FIG. 15.

FIG. 17A is an explanatory view of the bird's eye view in which adisplayed color of grid lines is the same as that of a road having a lowpriority order of displayed color.

FIG. 17B is an explanatory view of the bird's eye view in which aplurality of dots are painted over the road map in a modification of thefourth embodiment.

FIG. 18 is an explanatory view of an example of a gradation of abackground of the road map.

FIG. 19 is an explanatory view of an example of another gradation of abackground scenery of the road map.

FIGS. 20A and 20B are integrally an operational flowchart of a displaycontrol program of the road map as a modification of the fourthembodiment shown in FIGS. 16A and 16B.

FIG. 21 is an explanatory view for explaining a displayed example in thecase of the fourth embodiment in which the gradations are applied to thebackground scenery.

FIG. 22 is a schematic circuit block diagram of the vehicular navigatingapparatus in a fifth preferred embodiment according to the presentinvention.

FIG. 23 is an explanatory front view of a display panel in the case ofthe fifth embodiment shown in FIG. 22.

FIGS. 24A, 24B, and 24C are sequentially explanatory views forexplaining a series of operations for a joystick 10 shown in FIG. 22.

FIG. 25 is an operational flowchart for explaining an operation of a CPUshown in FIG. 22.

FIG. 26A is an explanatory view of a three-dimensional coordinate systemfor explaining a movement of a viewing point in the case of the fifthembodiment shown in FIG. 22.

FIG. 26B is an explanatory view of a three-dimensional coordinate systemfor explaining a movement of a tip of a line of sight vector in a sixthpreferred embodiment according to the present invention.

FIGS. 27A through 27E are explanatory views of the three-dimensionalcoordinate system for explaining movements of the viewing point and lineof sight direction in a seventh preferred embodiment according to thepresent invention.

FIG. 28 is an explanatory view of a display panel with a joystickomitted for explaining an alternative of the fifth, sixth, seven, andeighth embodiments of the vehicular navigating apparatus.

BEST MODE CARRYING OUT THE INVENTION

Reference will hereinafter be made to the drawings in order tofacilitate a better understanding of the present invention.

Before explaining first, second, third, fourth, fifth, sixth, andseventh preferred embodiments of an apparatus and method for navigatinga vehicle with a display unit according to the present invention, abasic concept of the invention will be described with reference to FIGS.3A, 3B and 4.

FIG. 3A and 3B show explanatory views for explaining a bird's eye view(E) from a predetermined position on an upper sky looking down to a roadmap as a viewing point to which the present invention is applicable.

The bird's eye view display is carried out as if the road map wereviewed from an upper sky looking down thereof and is widely used in, forexample, a flight simulation.

In FIG. 3A, a plane M denotes a road map and a rectangular shape a, b,c, and d denotes a displayed range through a display unit 5. Supposethat, in FIGS. 3A and 3B, a viewing point (E) is set on a position asshown in FIGS. 3A and 3B. The range of road map which can be viewedthrough the rectangular shape a, b, c, and d corresponds to a trapezoidregion A, B, C, and D shown in FIGS. 3A and 3B. That is to say, from theposition of the viewing point, a map data whose range is considerablywider than that of the rectangular shape a, b, c, and d can be viewed.In this way, the bird' eye view is displayed on the display image screenof the display unit 5 as if the shown trapezoid region A, B, C, and Dwere seen on its image from the position of the viewing point E of FIGS.3A and 3B.

FIG. 4 shows an example of the display of the bird's eye view on theroad map surrounding an optimally set route of travel from the presentposition of the vehicle to the destination (a position of the road mapto which the vehicle is finally to reach).

As shown in FIG. 4, the viewing point (E) is placed at the predeterminedposition of the upper sky in a direction opposite to the set destinationand from the viewing point (E) thus placed, a destination direction islooked down through its line of sight. When the viewing point is placedat such a position as described above, an image such that a reductionscale percentage of the road map is continuously increased as the eye isapproached nearly from the destination to the present position of thevehicle can be displayed as shown in FIG. 4. That is to say, theoptimally set route of travel can be displayed up to the place nearer tothe destination together with the surrounding position of the presentposition displayed in the extended scale form.

(First Embodiment)

FIG. 5 shows a schematic circuit block diagram of an apparatus fornavigating a vehicle using a display unit 5 in a first embodimentaccording to the present invention.

In FIG. 5, a direction sensor 1 is connected to an interface circuit 10and is arranged for, for example, detecting a geomagnetism at a positionat which the vehicle is present on the basis of the North direction soas to determine a forward direction of the vehicle. The direction sensor1 is exemplified by a U.S. Pat. No. 4,442,609 issued on Apr. 17, 1984 (,the disclosure of which is herein incorporated by reference).

A vehicle speed sensor 2 is connected to the interface circuit 10. Thevehicle speed sensor 2 is disposed on a power transmission output shaftand outputs a pulse train signal whose predetermined pulse number isvaried depending on a vehicle speed. A map storing memory 3 serves tostore a road map data including an intersection network data, the roadmap data further including positional information indicating nodesrepresenting the intersections, curved road points, and so forth, routepath lengths of roads connecting between the roads, and character dataincluding name of places.

A CPU (Central Processing Unit) 4 is connected to the interface circuit10 for preparing the bird's eye view display data on the road mapaccording to a series of processing shown in FIGS. 6 and 7 which will bedescribed later.

A ROM (Read Only Memory) 6 is connected to the interface circuit 10 andused for storing control program, for example, shown in FIGS. 6 and 7,to be executed by the CPU 4.

A RAM (Random Access Memory) 7 is connected to the interface circuit 10and used for storing a series of calculation results executed by the CPU4.

A V-RAM (Video RAM) 9 is connected to the interface circuit 10 and usedfor storing the bird's eye view display data prepared by the CPU 4, theviewing point of and line of sight of the bird's eye view to bedisplayed on the display unit 5 being changed according to the contentof the V-RAM 9.

An operator keyboard 8 is connected to the interface circuit 10. Theinterface circuit 10 is connected to every computer peripheral circuitelement described above.

It is noted that as soon as an operator (vehicle driver or occupant)operates an ignition key inserted into an ignition key switch of thevehicle to turn on either of ACC, IGN, or START portion of the ignitionkey switch of the vehicle, the CPU 4 starts the control routine shown inFIG. 6.

An operation of the first embodiment will hereinafter be described withreference to FIGS. 6 and 7.

At a step S1 of FIG. 6, the CPU 4 reads the destination at which thevehicle is finally to reach and which is input through the keyboard 8.

At a step S2 of FIG. 6, the CPU 4 measures the number of pulses per timeoutput from the vehicle speed sensor 2 or a pulse period of the pulsetrain of the vehicle speed sensor 2 so as to determine the running speedof the vehicle and measures the number of pulses so as to determine therunning distance for which the vehicle has run. Next, the CPU S2calculates a running trajectory on the basis of the forward direction ofthe vehicle detected by means of the direction sensor 1 and of thevehicle running distance and specifies the present position of thevehicle by means of a map matching technique between the runningtrajectory and road map data stored in the road map memory 3.

At a step S3, the CPU 4 calculates an optimum route of travel of thevehicle from a start point of the vehicle which is specified at the stepS2 to the destination by means of a well known Dikustra technique bysearching for the route of paths from the start point to thedestination. This Dikustra technique is exemplified by a Japanese PatentFirst Publication (Unexamined) No. Showa 62-86499 published on Apr. 20,1987 (or by U.S. Pat. No. 5,557,522, the disclosure of which is hereinincorporated by reference.)

At a step S4, the road map data surrounding the searched optimally setroute of travel is read from the road map data memory 3 on the basis ofthe calculated optimum route of travel by the CPU 4 and is stored in theRAM 7.

At a step S5, the CPU 4 determines a position of the viewing point todisplay the bird's eye view by means of the series of processing shownin FIG. 7. When the step S5 is processed, the road map range to bedisplayed on the display unit 5 is determined.

At a step S6, the CPU 4 transforms the road map data into the bird's eyeview data.

That is to say, as shown in FIG. 3A, the CPU 4 transforms the road mapdata within the trapezoid region A, B, C, and D into the bird's eye viewdata to be displayed on the display unit 5 according to the positionalrelationship between the position of the viewing point E, the positionof the rectangular shape of a, b, c, and d, and road map position.

The coordinate system transformation is such that the part of the roadmap corresponding to a side BC is displayed on a lower side of thedisplay unit 5, a part of the road map corresponding to a side AD isdisplayed on an upper side of the display unit 5, and, in addition, thereduction scale percentage is increased as the part of the imagecorresponding to the side AD becomes nearer to that corresponding to theside BC.

It is noted that, the horizontal distance of the position of the viewingpoint E with respect to the place M and its height in the Z axisdirection are defined so that, the sides BC and AB give 300 m and 10 Kmin their actual dimensions, respectively, and a distance from the sideCD to the side AD gives 10 Km in its actual dimension.

At a step S7, the CPU 4 stores the bird's eye view display data preparedat the step S6 into the V-RAM 9. Consequently, the road map within thetrapezoid region ABCD of FIG. 3A can be displayed on the display unit(display) 5 as shown in FIG. 8.

At a step S8, the CPU 4 reads character data on, for example, names ofplaces and name of intersections included in the road map data withinthe trapezoid region ABCD of FIGS. 3A and 3B and temporarily stores theV-RAM 9, thus character information such as names of places beingsuperimposed on the road map displayed on an image screen of the displayunit 5.

At a step S9, the CPU 4 calculates the present position of the vehiclefrom a running distance and a forward direction from the positiondetected at the step S2 using the direction sensor 1 and vehicle speedsensor 2.

At a step S10, the coordinate system of the present position of thevehicle calculated at the step S9 is transformed in the same way as thestep S6 so that the present position of the vehicle denoted by thevehicle mark data is stored into the V-RAM 9.

Consequently, as shown in FIG. 11 or FIG. 4, the arrow-marked presentposition of the vehicle is displayed.

At a step S11, a movement vector quantity of the vehicle upon thedisplay of the road map at the step S7, that is to say, a movementdirection and a movement distance are detected and if the movementvector quantity has exceeded a predetermined quantity, the routine goesto the step S4 so that an updating of the bird's eye view on the displayimage screen of the display unit 5 is carried out. Consequently, thesurrounding place around the present position of the vehicle is alwaysextensively displayed on a lower end area of the display image screen ofthe display unit 5 in the scale extended form and the rewriting of thebird's eye view to be displayed on the image screen of the display unit5 is carried out along with the running of the vehicle on the set routeof travel.

FIG. 7 shows a detailed processing flowchart of the step S5 in FIG. 6.

FIG. 9 shows an example of the road map data read out from the road mapmemory 3 at the above-described step S4 in which a hairpin curve, i.e.,U-shaped turning road forwarding in the direction opposite to that ofthe set destination is present on the set (optimum) route of travel tothe set destination denoted by a bold line.

The explanation of FIG. 7 will be described below with reference to FIG.9.

At a step S21 of FIG. 7, the CPU 4 determines a direction of a linesegment OD connecting the present position of the vehicle O detected atthe step S2 and set destination D read at the step S1, as appreciated,from FIG. 9.

At a step S22 of FIG. 7, the CPU 4 determines a direction of a straightline (V) (as shown in FIG. 9) which is perpendicular to the line segmentOD and is passing through the present position of the vehicle denoted byO in FIG. 9.

At a step S23, the CPU 4 detects a position of a crossing point Dcbetween the straight line (V) and optimum route, of travel L.

At a step S24 of FIG. 7, the CPU 4 derives each of an area Sm of atriangular region ODcD with each node Dm (wherein, 1≦m≦n, n denotes atotal number of the nodes) present on the part of the set (optimum)route of travel between the present position O of the vehicle and thecrossing point Dc as a vertex of the triangular region and with the linesegment ODc as a bottom side.

At a step S25, the CPU 4 determines a maximum value of the derived Sm(wherein, 1≦m≦n) at the step S24 and derives a height of itscorresponding triangular region from which the maximum value describedabove is determined, the height hmax being defined as a verticaldistance from the line segment ODc to the node Dm).

At a step S26, the CPU 4 determines a position of a point Dh hmax awayfrom the present position of the vehicle O and whose angle of directionis 180 degrees different from the set destination D.

At a step S27, the CPU 4 determines whether any point at which the linesegment ODh is intersected with the set route of travel L is present:

In the case of FIG. 9, since the line segment ODh is intersected withthe set route of travel L at the point K, the positive acknowledgment isdetermined at the step S27 and is transferred to a step S28.

At the step S28, the CPU 4 derives each area S1m of a triangular regionODhDm with each node Dm placed at a left side of the line segment ODh(wherein, 1≦m≦p, p denotes a total number of nodes present at the leftside of the line segment ODh) as its vertex and derives each area ofanother triangular region ODhDm with the line segment ODh as its bottomside and each node Dm (wherein, 1≦m≦q, q denotes a total number of nodespresent at the right side of the line segment ODh) as its vertex.

At a step S29 of FIG. 7, the CPU 4 determines the maximum values of theareas from each area S1m (wherein, is 1≦m≦p) and each area Srm (wherein,1≦m≦q). The CPU 4, then, heights of w1 and wr of the triangular regionsdetermined therein and derives a sum W of the heights w1 and wr. Then,the subroutine goes to a step S30.

At a step S30 of FIG. 7, the viewing point (E) of the bird's eye view isset at a position of an upper sky from which the road map including therange of the triangular region X in which the derived W at either thestep S29 or S32 are longitudinal length and lateral length can be lookeddown over.

For example, when the height w2 is larger than the height w1, as shownin FIG. 9, the upper sky above the point (E) shown in FIG. 9 and placedat the right side of the line segment ODh is set as the viewing point(E) of the bird's eye so as to enable the whole rectangular region X tobe looked down over.

As described above, in the first embodiment, the line of sight from theviewing point (E) of the bird's eye view is varied according to a lengthand direction of the hairpin curve on the set route of travel and thebird's eye view is displayed on the display image screen of the displayunit 5. Thus, all of the hairpin curves can be displayed thereon.

Although, in the first embodiment, the viewing point (E) is set at theposition so as to enable the whole rectangular region enclosing thehairpin curve to be viewed, the height of the viewing point and line ofsight direction may alternatively be varied according to the length anddirection of the hairpin curve.

For example, in the case where the hairpin curve is relatively long, thedisplayed region on which the set destination direction can be displayedbecomes narrower if all of hairpin curves on the set route of travel aredisplayed. In this case, only a part of the hairpin curve displayableregion may be displayed, for example, as shown in FIG. 4.

Alternatively, a special switch used to determine whether the operatordesires for the display unit 5 to display the hairpin curve region maybe alternatively installed so as to be connected to the interfacecircuit 10.

In addition, in place of the operation keyboard 8, a touch panel switchintegrated with the display unit 5 may be used. Furthermore, thekeyboard 8 may serve to directly input the set destination into theinterface circuit 10.

Although, in the first embodiment, the present position of the vehicleis specified using the direction sensor 1 and vehicle speed sensor 2,the present position of the vehicle may be determined according to theinput information through the keyboard 8. Or alternatively, a GPS(Global Positioning System) using electromagnetic waves from a pluralityof satellites may be used to specify the present position of thevehicle.

Although, in the first embodiment, the optimally (set) route of travelis derived from the calculation of the CPU 4 (step S3 of FIG. 6), thevehicle may be guided in accordance with an input route of travelprepared by the keyboard 8 and the bird's eye view can accordingly bedisplayed.

(Second Embodiment)

FIG. 10 shows a subroutine of the step S5 in a case of a secondpreferred embodiment of the vehicular navigation apparatus and methodaccording to the present invention.

It is noted that the main routine of the second embodiment is the sameas shown in FIG. 6 and its hardware structure is the same as shown inFIG. 5.

At a step S210 of FIG. 10, the CPU 4 divides the coordinate transformeddata of the step S6 into two classes, i.e., the road network image dataand character data representing the names of places and stores them intothe RAM 7, respectively. Here, the coordinate position informationrepresenting at which position on the display image screen therespective data are displayed is also stored.

At a step S220 of FIG. 10, the CPU 4 determines whether all of thecharacter data to be displayed on a lower half of the display imagescreen have been displayed on the display image screen of the displayunit 5 from among the character data stored in the RAM 7.

If No at the step S220, the subroutine goes to a step S230 in which thecharacter data not yet to be displayed on the display image screen ofthe display unit 5 are stored in a predetermined region of the V-RAM 9which corresponds to the display position of the display unit 5. It isnoted that the storage region of the V-RAM 9 corresponds exactly to thedisplay region of the image screen of the display unit 5. If the dataare stored in the predetermined region of the V-RAM 9, the data storedthereinto are displayed onto the part of the display region whichcorresponds to the storage region described above. Hence, at theprocessing of the step S230, the character data are displayed onpredetermined regions of the lower part of the display image screen.

When the processing at the step S230 is ended and when all of thecharacter data have been displayed on the lower half of the displayimage screen the subroutine returns to the step S240. At the step S240,the CPU 4 stores a part of the road network image data stored in the RAM7 which is to be displayed on a lower half of the display image screeninto the corresponding region of the V-RAM 9. Consequently, the roadnetwork image data are written onto the displayed character datadisplayed on the display unit 5 as appreciated from FIG. 11.

At a step S250, the CPU 4 determines whether all of the road networkdata to be displayed on the lower half of the display image screen havebeen displayed on the display image screen of the display unit 5. If Noat the step S250, the subroutine returns to the step S240 and if Yes atthe step S250, the subroutine goes to a step S260.

At the step S260, the CPU 4 determines whether the part of the roadnetwork image data to be displayed on the upper half of the displayimage screen has already been displayed on the display image screen.

If No at the step S260, the subroutine returns to a step S270 and theroad map image data which is not yet displayed on the display imagescreen is stored into a corresponding region of the V-RAM 9.

When the process at the step S270 is ended, the subroutine returns tothe step S260 in which the CPU 4 determines that the road network datahas been displayed on the upper half of the display image screen and thesubroutine returns to the step S280.

At the step S280, the, character data to be displayed on the upper halfof the display image screen is stored into the corresponding region ofthe V-RAM 9. Consequently, the character data are written onto the roadnetwork image data already displayed on the display image screen of thedisplay unit 5, as shown in FIG. 11.

At a step S290, the CPU 4 determines whether all of the character datato be displayed on the upper half of the display image screen havealready been displayed. If No at the step S290, the subroutine returnsto a step S280. If Yes at the step S280, the processing of FIG. 10 isended.

In the second embodiment, since the road network data is written ontothe character data on the road map at the display region of lower halfof the display image screen at which the surrounding area around thepresent position of the vehicle is essentially displayed, the roadnetwork can be viewed and recognized in details even if both of thecharacter data and road network image data are superimposed together. Onthe other hand, since the character data are written onto the roadnetwork image data at the display region of the upper part of thedisplay image screen at which the direction of the set destination isindicated, the direction toward the set destination can be recognized bythe character thereof. FIG. 11 shows, an example of the bird's eye viewof the road map carried out in the case of the second embodiment.

Although, in the second embodiment, the upper writing order is switchedbetween the road network image data and the character data, theswitching therebetween may be carried at the position except theintermediate (i.e., upper and lower halves) position or at whichposition the switching is carried out may be arbitrarily selected. Oralternatively, the switching position may automatically be determinedaccording to a density of the road networks to be displayed on thescreen and displayed map range.

Furthermore, the upper writing order may be changed according to, forexample, a distance from the present position of the vehicle,

That is to say, in a case where the part of the road map from thepresent position within a predetermined distance is to be displayed, theroad network data may be written onto the character data and in a casewhere the part of the road map exceeding the predetermined distance isdisplayed, the character data may be written onto the road network imagedata. It is noted that the predetermined distance described above maycorrespond to the boundary between the upper half and lower half of thedisplay image screen.

It is also noted that since when the road network data are written ontothe character data, it is not easy to recognize or to read the characterdata, a display color of the road network data at the overlapped (orsuperimposed) parts may be changed so that the colors of both characterdata and that position of the road network image data are different.

Although, in the second embodiment, the bird's eye view is displayed onthe image screen of the display unit, it is possible to smoothly guidethe vehicle with the road network image data on the surrounding of thepresent position of the vehicle displayed with a priority in a casewhere a normal top viewed road map data is displayed in place of thebird's eye view.

(Third Embodiment)

FIG. 14 shows an explanatory view how the range of the road mapdisplayed on the display image screen is varied when a line of sightdirection of the bird's eye is varied for each of 30°. Each of trapezoidregions EFGH, IJKL, and MNOP denotes a road map range to be displayed onthe display image screen in each of the lines of sights of the bird'seye views.

Although a length of the distance of the set route of travel LL shown inFIG. 14 and displayed on the image screen which provides the maximumcorresponds to the trapezoid region ABCD shown in FIG. 13 (or FIGS. 3Aor 3B), the length of the set route of travel displayed within eachtrapezoid region is accordingly varied if the general direction of thewhole set route of travel is different. That is to say, if the bird'seye view is displayed without consideration of the general direction ofthe set route of travel, the set route of travel cannot be displayedwith a sufficient length thereof.

FIG. 12 shows a subroutine of the step S5 shown in FIG. 6 in a case of athird preferred embodiment according to the present invention.

The main routine of the third embodiment is the same as that shown inFIG. 6 of the first embodiment and the hardware structure of thevehicular navigation apparatus in the third embodiment is the same asshown in FIG. 5.

It is noted that at the step S6 of FIG. 6, the CPU 4 carries out thecoordinate system transformation of the road map data within the rangeof the trapezoid region ABCD according to the position of the viewingpoint E and positional relationship between the position of therectangular abcd and road map position into the data to be displayed onthe display image screen of the display unit 5. Specifically, the partof the road map at a side BC is displayed on a lowest side of thedisplay image screen of the display unit 5 and the part of the road mapat a side AD is displayed on an upper side of the display image screen.In addition, the reduction scale percentage becomes large as theposition approached from the side AD to the side BC. It is noted thatthe viewing point position and height of the viewing point are definedsuch that, for example, the sides of BC and AB are 300 m and 10 Km intheir actual dimensions and the distance from the side CD to the side ABis 10 Km in the actual dimension.

It is also noted that when the series of processing of FIG. 12 areexecuted, the viewing point S is set on an upper sky in a direction of(180°+θ°) with the North direction of the road map as θ=0° and on anupper sky above a point T which is remote a predetermined distance fromthe present position of the vehicle G, as shown in FIG. 13. Then, therectangular region abcd indicating the display range is set at apredetermined position between the viewing point S and present positionof the vehicle G.

At a step S21A of FIG. 12, the CPU 4 initializes such that θ=0° andtotal values Lθ (wherein, θ=0°, 30°, - - - , 300°) of the path lengthsof route links are all zeroed. The term route links denote roads (links)connecting between the adjacent nodes on the set route of travel. In thethird embodiment, the route links of m-th numbers on the set route oftravel are denoted by l₁ through l_(m) in the order from the presentposition to the destination.

At a step S22A, a variable n is set to zero. The variable n denotes avariable to specify one of the route links on the set route of travel.That is to say, l_(n) denotes the n-th number route link from thepresent position of the vehicle.

At a step S23A, the CPU 4 reads the road map data in a range of the roadmap which can be viewed through the rectangular abcd, with the line ofsight directed toward the direction θ from the viewing point position.

That is to say, the CPU 4 reads the road map data in the range of thetrapezoid region ABCD shown in FIG. 13.

At a step S24A, the CPU 4 determines whether the data related to theroute link l_(n) in the road map data read at the step S23A, that is tosay, determines whether the route link l_(n) can be displayed on thedisplay image screen of the display unit 5 when the bird's eye view isdisplayed with the line of sight direction set as θ.

If the determination is acknowledged at the step S24A, the subroutinegoes to a step S25A in which the path length of l_(n) is added to thetotal value of the route path length Lθ. Then, the subroutine goes to astep S26A. On the other hand, if the determination is not positiveacknowledgment at the step S24A, the subroutine goes to the step S26A inwhich the variable n is added to one.

At a step S27A, the CPU 4 determines whether the variable n is largerthan m indicating the total number of the route links.

If No at the step S27A, the subroutine goes to the step S24A and if Yesat the step S27A, the subroutine goes to a step S28A. At the step S28A,the line of sight direction θ is added to 30°.

At a step S29A, the CPU determines whether θ=360°. If No at the stepS29A, the subroutine returns to the step S22A. If Yes at the step S29A,the subroutine goes to a step S30A. At the step S30A, the CPU 4 selectsone of the total values which is largest from the respective routelengths of L0, L30, L60, - - - , L330. The corresponding angle of θ isstored in the RAM 7. Then, this subroutine is ended.

In the third embodiment shown in FIG. 12, the direction of line of sightis varied for each 30 degrees, the total values of the route pathlengths of the route links displayed on the display image screen of thedisplay unit 5 are derived for the respective directions of the line ofsight, and one of the directions of line of sight is automaticallyselected which provides the displayed longest set route of travel.

Although, in the third embodiment shown in FIG. 12, the comparison ofthe total values of the route lengths on the set route of travel Lθ withthe directions of the line of sights varied for each 30°, the value ofthe angle may not be fixed as 30°.

The alternatives of the third embodiment are generally the same as thosedescribed in the first embodiment.

(Fourth Embodiment)

FIG. 15 shows the vehicular navigating apparatus in a fourth embodimentaccording to the present invention.

Although the vehicular navigating apparatus shown in FIG. 15 isgenerally the same as that shown in FIG. 5, the hardware structure willbe explained with reference to FIG. 15.

A GPS receiver 1A is connected to a controller 6A for measuring thepresent position of the vehicle using a GPS navigating method byreceiving signal electric waves from the satellites. The GPS receiver 1Ais exemplified by the U.S. Pat. Nos. 4,743,913 issued on May 10, 1988and 4,899,285 (, the disclosure of which are herein incorporated byreference,) so as to detect the present position of the vehicle, forwarddirection of the vehicle, and running velocity.

The vehicle speed sensor 2A is the same as the vehicle speed sensor 2 ofFIG. 5. The direction sensor 3A is the same as the direction sensor 1 ofFIG. 5. A CD-ROM 4A detects a road map data and corresponds to the roadmap memory 3 of FIG. 5. A keyboard section 5A corresponds to thekeyboard 8 of FIG. 5 and is provided with various operating members toset the present position, set the destination, and to scroll thedisplayed road map.

The controller 6A is connected with the display unit 7A, ROM 8A, RAM 9A,and V-RAM 10.

The controller 6A includes a microcomputer and its peripheral equipment.

In the fourth embodiment, color classification is carried out in such away that freeways (autobahns in German) are in blue, national highwaysare in red, (regional) normal highways are green, principal roads are inyellow, and streets are in gray in accordance with displayed colors usedcommonly in a generally available road map book and a display priorityorder of the roads classified above is such an order as freeways,national highways, normal highways, principal roads, and streets.

In addition, in the fourth embodiment, so-called grid lines (in-linearrangement) are superimposed on the road map at each predeterminedinterval of space together with the road map in the form of bird's eyeview on the display image screen.

It is noted that the grid lines on the bird's eye view do not exactlycorrespond to the in-line arrangement shape such that the intervalsbetween each one line of the grid lines and adjacent lines of the gridlines become narrower as the displayed part on the bird's eye viewbecomes away from the present position of the vehicle and a displaydensity of the grid lines becomes high at a displayed part of thedisplay screen near to the set destination. Hence, at the displayed partof the display screen near to the set destination, a viewer of thedisplay unit 7A can view the displayed part as if a background of theroad map were painted over by the display color of the grid line. Eachinterval of the grid line can arbitrarily be set according to the regionof the road map displayed on the display unit 7A. For example, 100 mminterval may be appropriate.

Furthermore, in the fourth embodiment, the display color of the gridlines is the same as that of a road having a lowest display priorityorder. For example, one of the ranks of the roads which has the lowestdisplay priority order is the streets so that the display color of thegrid lines is gray as the same as the streets.

As described above, the display density of the displayed color of thegrid line becomes high at the display part near to the set destinationin the bird's eye view so that the viewer can view the displayed part asif it were painted wholly by the color of gray. Therefore, the streetsdisplayed in gray are hidden in the grid line of the same color as grayand the viewer can view that displayed part as if it did not display thestreets.

Next, FIGS. 16A and 16B show integrally a display control operationalflowchart in the fourth embodiment.

When a main switch of the keyboard section 5A is turned on, themicrocomputer of the controller 6A starts the execution of the programshown in FIGS. 16A and 16B.

At a step S1A of FIG. 16A, the microcomputer calculates the presentposition of the vehicle by means of a self contained navigating methodand/or GPS navigating method.

At a step S2A of FIG. 16A, the microcomputer compares the presentposition of the vehicle calculated at the present time and thatcalculated at a previous time so as to determine whether the vehicle hasmoved.

If the microcomputer has determined that the vehicle has moved, theroutine goes to a step S3A. If not at the step S2A, the routine returnsto the step S1A.

At the step S3A, the microcomputer reads the road map data surroundingthe present position of the vehicle from the CD (Compact Disc)-ROM 4A.It is noted that the range of the road map to be read from the CD-ROM 4Ais previously set according to a displayable range (size) of the displayunit 7A and memory capacities of the RAM 9A and V-RAM 10A.

At a step S4A, the read road map surrounding the present position of thevehicle is written into the RAM 9A in a predetermined painting form. Atthis time, the roads on the road map are classified in different colorsaccording to the ranks of the roads described above.

At a step S5A, the grid lines having the predetermined interval of spaceare written in a gray color of display on the road map in the RAM 9A.

The display color of the grid lines is the same as that of the streetsto be vanished at a display part of the display image screen of thedisplay unit 7A in the bird's eye view which is far way from the presentposition of the vehicle (normally, near to the set destination).

At a step S6A, the microcomputer calculates the viewing point (E), thedirection of line of sight (EF), and an angle of field of view of thebird's eye view to draw the road map in the form of the bird's eye view.In the fourth embodiment, the viewing point position and field of viewangle are set such that the present position of the vehicle is placed ata center of a horizontal direction (left and right) of the display imagescreen of the display unit 7A and at a position near to a lower end of avertical direction (upward and downward) of the display image screen ofthe display unit 7A. It is noted that the direction of line of sight isset in such a direction as the vehicular forward direction or as thedirection of the set destination.

At a step S7A, the microcomputer transforms in the coordinate system ofthe road map according to the viewing point, angle of field of view, anddirection of line of sight set at the step S6A.

At a step S8A, the road map transformed in the coordinate system iswritten into the RAM 10A. At a step S9A, the mark representing thepresent position of the vehicle is written onto the transformed roadmap.

At a step S10A, the road map thus written in the RAM 10A is drawn ontothe display image screen of the display unit 7A and the routine returnsto the step S1A.

FIG. 17A shows one of the display image screen executed in the fourthembodiment.

As shown in FIG. 17A, the display color of the grid line to be writtenonto the road map in the form of the bird's eye view is the same as thedisplay color of the city or town streets having a lowest displaypriority. Therefore, as shown in FIG. 17A, the streets placed remotelyfrom the present position are substantially hidden in the grid line andcannot clearly be viewed so that the road map can be easier to be viewed(legible).

However, alternatively, the display color of the grid line may bedifferent from that of the rank of road which has the lowest priorityorder and the display color of each crossing point of the mutual gridline may be the same as that of the rank of the roads having the lowestdisplay priority order. In this way, it becomes easier to distinguishthe rank of road having the lowest priority order from the grid line atthe part of road map surrounding the present position of the vehicle andthe crossing points of the mutual grid lines are concentrated at thepart of the road map remotely placed from the present position of thevehicle so that the roads having the lowest display priority order areburied and hidden into the crossing points and the road map becomeseasier to be viewed.

In addition, as shown in FIG. 17B, with no grid line displayed on theroad map, a plurality of dots (points), having one of the same class ofcolors as the display color of at least one rank of the roads, may bepainted coarsely at the part of the road map surrounding the presentposition of the vehicle and may be painted finely at the remaining partof the road map which is remote from the present position of thevehicle. In this way, it becomes easier to distinguish the plurality ofpoints (dots) from the roads having the lowest display priority order atthe display part of the road map surrounding the present position of thevehicle. On the other hand, at the remaining part of the road map whichis remote from the present position of the vehicle, the display imagecan be viewed as if the background were painted over by the displaycolor of the plurality of points (dots) and the roads of the rank havingthe lowest display priority order were buried and hidden into theplurality of points (dots). Thus, the road map can be easily viewed andrecognized.

FIGS. 18 and 19 show modifications of the fourth preferred embodiment inwhich a gradation of color hues and/or tones is carried out such that abackground color of the road map approaches one of the same class ofcolors as that of the roads having the lowest (or lower) displaypriority order as the display image part of the image screen becomesnearer to the remotest position of the displayed part of the imagescreen from the present position of the vehicle.

Such a gradation as described above may be carried out in the directionof the line of sight as appreciated from FIG. 18.

Such a gradation as described above may be carried out in a concentricform with the present position of the vehicle as the center asappreciated from FIG. 19.

The hardware structure of the modifications described above is the sameas shown in FIG. 15.

FIGS. 20A and 20B show integrally the display control operationalflowchart of each modification of the fourth embodiment of the vehicularnavigating apparatus according to the present invention.

It is noted that the same steps of FIGS. 20A and 20B as those shown inFIGS. 16A and 16B are executed in the same ways and, hence, thedifferent step of a step S21B will be described below.

That is to say, after the microcomputer determines that the vehicle hasmoved at the step S2A, the routine goes to the step S21B.

At the step S21B, the gradation as shown in either of FIG. 18 or 19 iscarried out to process the background of the road map on the displayedimage screen of the display unit 7A before the road map is displayed onthe screen. It is noted that it is of course that the display unit 7Acomprise a full color liquid crystal display device in the same way asin the case of the fourth embodiment.

Upon completion of the background processing, the routine goes to thestep S3A and the same series of processing as that shown in FIGS. 16Aand 16B is carried out. It is noted that in each of the modificationsthe grid line is not drawn onto the road map.

In each of the modifications of the fourth embodiment, the backgroundcolor of the road map receives the gradation of either of the color huesor tones such that as the displayed part of the display image screen ismore remote from the present position of the vehicle, the backgroundcolor approaches one of the same class of colors as the display color ofthe streets having the lowest display priority order. Hence, as shown inFIG. 21, parts of streets placed at a portion of the displayed road mapremote from the present position of the vehicle are buried and hiddeninto the background of the road map so that the road map can easily berecognized.

As described above, since, in the fourth embodiment, the grid lineshaving one of the same class of colors as the display color with whichat least one rank of roads is painted (or drawn) on the road map in theform of the bird's eye view displayed in colors different according toeach rank of the roads; the roads which fall in the rank having thecolor of the same series of colors as the grid line are buried andhidden into the grid line at the part of the display image screen of thedisplay unit which is remote from the present position of the vehicle sothat the display image screen can be viewed as if such a rank of roadsas described above were not displayed. In other words, at the displayedpart of the image screen which is remote from the present position ofthe vehicle, the arbitrary rank of the roads which is not desired to bedisplayed cannot be viewed. Consequently, it is not necessary todecimate or omit such a rank of roads from the displayed part of thedisplay image screen which is remote from the present position of thevehicle. Then, the road map in the form of the bird's eye view canprovide an appropriate road density from the part of the road mapsurrounding the present position of the vehicle to the set destination.

As described above, since, in the fourth embodiment, the grid lines arepainted (or drawn) in one of the same classes of colors as the displaycolor of the rank of the roads having the lowest display priority order,even the streets having the lowest display priority order can visuallybe recognized at the displayed part of the image screen which surroundsthe present position and the remaining ranks of roads such as freewaysand national highways can visually be recognized at the remaining partof the display image screen which is remote from the present position ofthe vehicle with the rank of the roads which has the lowest displaypriority order buried and hidden into the grid lines.

As described above, since, in the fourth embodiment, the grid lines arepainted (or drawn) on the road map in the form of the bird's eye viewwhose crossing points have one of the same class of colors as thedisplay color of at least one rank of the roads; the rank of the roadswhose display color is one of the same class of colors as that of thecrossing points of the grid line is buried and hidden into the crossingpoints at the displayed part of the image screen which is remote fromthe present position of the vehicle so that the rank of the roaddescribed above cannot visually be recognized thereat. The sameadvantages as described above can be achieved.

In addition, in the fourth embodiment, the crossing points of the gridline are painted (or drawn) in one of the same class of colors as thedisplay color of the rank of the roads whose display priority order islowest. The same advantages as described above can be achieved.

In addition, in the fourth embodiment, the background of the road map ispainted (or drawn) in one of the same class of colors as the displaycolor of at least one rank of the roads. The same advantages asdescribed above can be achieved.

In addition, in the fourth embodiment, the background of the road map ispainted (or drawn) in one of the same class of colors as the displaycolor of the rank of the roads whose display priority order is lowest.The same advantages as described above can be achieved.

In addition, in the fourth embodiment, the background is painted (ordrawn) in the color gradation form (color hue and/or color tone) suchthat the background color of the part of the displayed road map which isremote from the present position of the vehicle becomes one of the sameclasses of colors as the display color of at least one rank of theroads. The same advantages as described above can be achieved.

In addition, in the fourth embodiment, the plurality of points (dots)are painted on the road map in the form of the bird's eye view so thatthe dots located at a surrounding portion of the present position of thevehicle become coarse and those located at a portion of the displayedroad map which is remote from the present position of the vehicle becomefine. The same advantages as described above can be achieved.

Furthermore, in the fourth embodiment, the plurality of points (dots)are painted on the road map in the form of the bird's eye view havingone of the same class of colors as the display color of the rank of theroads whose display priority order is lowest. The same advantages asdescribed above can be achieved.

(Fifth Embodiment)

FIG. 22 shows a schematic circuit block diagram of a fifth embodiment ofthe vehicular navigating apparatus according to the present invention.

The hardware structure of the fifth embodiment shown in FIG. 22 isgenerally the same as the first embodiment as shown in FIG. 5 except theaddition of a joystick 100.

The joystick 100 is provided for scrolling the road map data on thedisplay screen 80 of the display unit 5 as shown in FIG. 23. The displayunit 5 is provided with the keyboard 8 located aside from the displayimage screen 80 to serve to input the destination and the joystick 100.

As shown in FIG. 23, elastic member made of a rubber or spring denotedby 11 is attached onto a lower end of the joystick 100 which isconnected to an upper surface of a display panel 12. A handle 13 havinga ball shape is disposed on a tip of the joystick 100.

The joystick 100 can be rotated in a semispherical shape with its lowerend as the center. Its rotation variable can indicate respectiveoperating variables in an X-axis direction and Y-axis direction.

For example, suppose that the joystick 100 is rotated through an angleof θ with respect to a Z-axis and through an angle of φ with respect tothe X-axis.

At this time, the operating variable ΔX in the X-axis direction and thatΔY in the Y-axis direction are expressed as in the following equations(1) and (2).

    ΔX=L·sinθ·cosφ           (1),

    ΔY=L·sinθ·sinφ           (2).

In addition, when the joystick 100 is operated in the Z-axis direction,the elastic member 11 located on the lower end of the joystick 100 isexpanded or reduced so that the operating variable in the Z-axisdirection is indicated according to a displacement of the joystick 100caused by the expansion or shrinkage of the elastic member 11.

For example, when the joystick 100 is pushed by Z1 in a negativedirection with respect to the Z-axis direction, namely, as shown in FIG.24B, toward the direction to the display panel 12 by Z1, the operatingvariable ΔZ of the joystick 100 is expressed as:

    ΔZ=Z1                                                (3)

FIG. 25 shows an operational flowchart executed by the CPU 4 in the caseof the fifth preferred embodiment according to the present invention.

In same way as in the case of the first embodiment, when the vehicularignition key is turned to either of the ACC, IGN, or START position, theprogram shown in FIG. 25 is started with the destination set by theoperator through the keyboard 8 shown in FIG. 22.

Steps S1B, S2B, and S3B of FIG. 25 correspond to the steps of S1, S2,and S3 of FIG. 6, respectively.

Referring to FIG. 27A, at a step S4B of FIG. 25, the CPU 4 specifies theviewing point E and direction of line of sight EF when the bird's eyeview is to be displayed.

Before the joystick 100 is operated, suppose that the present positionof the vehicle on the road map is set as a tip F of the direction ofline of sight and a position of the upper sky in a direction opposite tothe set destination with the present position of the vehicle as thereference and from which the direction of the present position of thevehicle is looked down over is set as the viewing point E from which the(optimally set) recommended route of travel can be viewed with themaximum length of the route of travel, as appreciated from FIG. 3B.

In the fifth embodiment, a vector indicating the direction of line ofsight EF is called a line of sight direction vector and an underline isdrawn to represent the vector quantity in a sense to distinguish it froma scalar quantity.

At a step S5B, the CPU 4 calculates the range of the road map displayedon the image screen of the display unit 5. That is to say, the CPU 4determines where the part of the road map the trapezoid ABCD shown inFIG. 3B corresponds to.

At a step S6B, the CPU 4 reads the road map data in the range calculatedat the step S5B from the road map memory 3.

At a step S7B, the CPU 4 transforms the road map data read at the stepS6B into the bird's eye view display data. The CPU 4 transforms the roadmap data within the range of the trapezoid ABCD of FIG. 3A into theimage data so as to reduce and display the image date within arectangular abcd of FIG. 3B indicating the displayed region. Here, therecommended route of travel is the image data whose color is differentfrom the normal road map data (top view road map) and the position inthe bird's eye view corresponding to the present position of the vehicleis marked with the vehicle arrow mark synthesized with the bird's eyeview data.

At a step S8B of FIG. 25, the image data prepared at the step S7B istransferred into the V-RAM 7. Thus, the road map data within thetrapezoid ABCD is transformed into the bird's eye view display data andis displayed on the image screen of the display unit 5.

At a step S9B, the CPU determines whether the vehicle has moved by thepredetermined distance.

If Yes at the step S9B, the routine returns to the step S4B in which theCPU 4 selects the same viewing point E and direction of line of sight asthose of the bird's eye which has been displayed at the time immediatelybefore the vehicle stops.

If No at the step S9B, the routine goes to a step SLOB in which the CPU4 determines whether the joystick 100 has been operated. If No at thestep S10B, the routine returns to the step S9B.

If No at the step S10B, the routine goes to a step S11B.

At the step S11B, the CPU 4 calculates the operating variables (ΔX, ΔY,ΔZ) of the joystick 100 on the basis of the calculation formulae (1)through (3).

Thereafter, the CPU 4 calculates the scroll quantity (Sx, Sy, Sz) on thebasis of the following formulae (4) through (6). It is noted thatcoefficient k1 in the formulae (4) through (6) denotes a positiveconstant.

    Sx=k1·ΔX                                    (4),

    Sy=k1·ΔY                                    (5),

    Sz=k1·ΔZ                                    (6).

In the formulae (4) through (6), the common coefficient k1 is multipliedby ΔX, ΔY, and ΔZ. Alternatively, a different coefficient for eachdirection may be multiplied as expressed as follows:

    Sx=kx·ΔX                                    (7),

    Sy=kx·ΔY                                    (8),

    Sz=kx·ΔZ                                    (9).

At a step S12B, the CPU deviates the viewing point E by the calculatedscroll quantity at the step S11B.

For example, when the joystick 100 is operated by ΔX in the X-axisdirection, a point Ex to which the viewing point E is moved by Sx in theX-axis direction is set as the viewing point position, as shown in FIG.26A.

In addition, the direction of line of sight in this case is a vector ofExFx of FIG. 26A which is parallel to the old direction of line of sightEF. Similarly, when the joystick 100 is operated in the Y-axis directionby ΔY and in the Z-axis direction by ΔZ, respectively, the viewing pointE is moved to Ey and Ez as shown in FIG. 26A.

When the process at the step S12B is ended, the routine returns to thestep S5B in which the CPU 4 rewrites the bird's eye view display.

In the fifth embodiment, the position of the viewing point E is deviatedaccording to the operation through the joystick 100 so that the viewingpoint E can arbitrarily be varied and the road map having an arbitraryrange can be displayed on the image screen of the display unit 5.

In addition, since the direction of line of sight can be translatedaccording to the operation of the joystick 100, the map area to bedisplayed on the display image screen of the display unit 5 can becommon wherever the viewing point is set. Consequently, the distancerelationship on the route of travel and destination can easily begrasped.

Furthermore, in the fifth embodiment, the viewing point E is moved inthe direction toward which the joystick 100 is operated so that thebird's eye view is easily coincident with the operator's sense offeeling and the display along with the operator's intention can becarried out.

(Sixth Embodiment)

In a sixth embodiment, the position of the tip F of the line of sightvector EF is varied according to the movement of the joystick 100.

The structure and flowchart of the sixth embodiment are the same asthose in the fifth embodiment except the step S12B of FIG. 25.

FIG. 26B shows the movement of the tip F of the line of sight vector EFin the case of the sixth embodiment.

When the movement of the joystick 100 indicates the scroll quantity Sxin the X-axis direction, a point Fx to which the tip F of the line ofsight vector is moved in the X-axis direction by Sx is a new tip F ofthe line of sight vector as shown in FIG. 26B. Similarly, when thejoystick 100 is moved by ΔY and LZ, respectively, in the Y direction andZ direction, the tip F of the line of sight vector is moved to Fy andFz, respectively.

In the sixth embodiment, the line of sight is varied according to theoperation of the joystick 100 with the viewing point position fixed.Thus, it is convenient for the operator (vehicular occupant) torecognize or check to see, for example, the road map surrounding to thepresent position of the vehicle through the display unit 5.

In addition, since the operation direction of the joystick 100 iscoincident with the movement direction of the tip of the direction ofline of sight, it is coincident with the operator's sense of feeling anddisplay in accordance with the operator's intention can be carried out.

(Seventh Embodiment)

In a seventh preferred embodiment of the vehicular navigating apparatus,the viewing point is rotated in accordance with the operation of thejoystick 100 and a mode switching means is provided. When the mode isswitched by means of the mode switching means, the tip F of the line ofsight vector is moved (translated) or rotated according to the operationof the joystick 100.

The difference from the fifth and sixth preferred embodiments is onlythe step S12B of FIG. 25.

FIGS. 27A, 27B, 27C, and 27D show the operation example of the joystickand coordinate system of the viewing point and line of sight vector forexplaining the operation in the case of the seventh embodiment.

Suppose that, in FIGS. 27A through 27D, the X-axis component of the lineof sight vector EF is zero and the Y-axis component of the line of sightvector EF is R.

In the seventh embodiment, the viewing point E is rotated along an outerperiphery (dotted portion of FIG. 27A) of a circle C having a radius Rwhich is parallel to the place XY, as shown, in FIG. 27A.

Specifically, when the joystick 100 is operated by ΔX in the positivedirection of X axis, the viewing point E is rotated along the circle Cin a negative direction of X axis by k2·ΔX (k2>). Then, suppose that aline segment connecting the viewing point E' after the rotation and apoint F is a new line of sight vector E'Y.

Since, in the seventh embodiment, the viewing point E is rotated in thedirection opposite to the direction toward which the joystick 100 isoperated, the line of sight direction is always coincident with thedirection of the operation of the joystick 100.

On the other hand, when the joystick 100 is operated in the Z-axisdirection, the viewing point E is moved on a prolongation of the line ofsight vector EF.

For example, when the joystick 100 is operated in a negative directionof the Z axis, i.e., when the joystick 100 is pushed toward the displaypanel 12, the viewing point E is moved to a position near the point F,for example, to a point A of FIG. 27B. Hence, as the pushing force onthe joystick 100 becomes stronger, the road map becomes extended. On thecontrary, when the joystick 100 is pulled in the positive direction ofthe Z axis, the viewing point E is moved away from the point F. Hence,as the pulling force on the joystick 100 becomes stronger, the road mapbecomes reduced.

In addition, when the joystick 100 is pulled to some degree in thepositive direction of Z axis, the viewing point E is moved in thepositive direction of the Z axis, i.e., to a point B shown in FIG. 27B.Consequently, the display unit 5 displays the road map which can beviewed from the upper sky straight above the road map, i.e, the normaltop view of the road map.

FIG. 27C shows a situation wherein the range of the road map displayedon the display image screen of the display unit 5 is varied according tothe operation of the joystick 100 in the direction of the Z axis.

When the viewing point is placed at points A, E, and B shown in FIG.27B, respectively, the respective ranges of the road map to be displayedare denoted by A1, B1, and E1 shown in FIG. 27C.

The reduction scale percentage of the bird' eye view is arbitrarilyvaried according to the operation of the joystick 100 in the directionof Z axis. In a case where the joystick 100 is pulled to some degreeaway from the display panel, the display is such that the road map isviewed from the direction of the upper sky near the straight above theroad map, i.e., approximately the top view.

On the other hand, after the joystick 100 is operated in the directionof either -Y or +Y, it is operated in the direction of Z axis. At thistime, the line of sight vector tip F is moved according to the operatingvariables of the joystick 100 in place of the movement of the viewingpoint E.

In details, the mode switching is instructed according to the operationof the joystick 100 in the direction of Y axis so that the scrollingmethod in the case where the joystick 100 is operated in the directionof X axis is varied.

For example, when the joystick 100 is operated in the X axis directionby ΔX, the tip F of the line of sight vector is moved by k3·ΔX in thedirection of X axis in parallel to the X axis as shown in FIG. 27D.Thus, with the position of the viewing point E fixed, only the positionof the tip F of the line of sight vector can be varied.

It is noted that, in place of the movement of the position of the tip Fof the line of sight vector, the tip F of the line of sight vector maybe rotated in accordance with the operation of the joystick 100 as shownin FIG. 27E.

As described above, since the operation of the joystick 100 permitsrotation of the viewing point E, movement of the viewing point E on theline of sight vector, and movement of the tip F of the line of sightvector, in the seventh embodiment, a more flexible scrolling can beachieved.

In addition, since only the operation of the joystick 100 in thedirection of X axis permits the rotation of the viewing point E, theviewing point E can be rotated even if an inexpensive joystick such asto enable the movement thereof in the direction of only X axis.Consequently, the cost-effective vehicular navigating apparatus can beachieved.

Furthermore, since the mode switching can be made according to thespecific operation, for example, the operation in the Y-axis directionof the joystick 100, no switch is needed to switch the mode and, hence,the cost effective vehicular navigating apparatus can be achieved.

(Eighth Embodiment)

In an eight preferred embodiment, the scrolling of the displayed imageroad map is carried out according to a magnitude of a torsional forceacted upon the joystick (hereinafter, referred to as a torsionquantity).

FIG. 24C shows a contour of the joystick 100A in the case of the eighthembodiment.

The joystick 100A has the same profile as that 100 of the fifth toseventh embodiments but can be twisted with the Z axis as the center.The CPU 4 can detect the torsion quantity when the joystick 100A istwisted. The torsion quantity can be detected by counting a number ofpulses in a pulse train signal which is generated from a pulsegenerating member provided on a lower end of the joystick 100A wheneverthe joystick 100A is twisted by a predetermined quantity.

The difference in the eight embodiment from the fifth embodiment is thestep S12B of FIG. 25.

In the eighth embodiment, the position of the viewing point E is movedin accordance with the operating variables of the joystick 100A in thesame way as in the case of the fifth embodiment described above.

However, in the eighth embodiment, when the joystick 100A is twisted andthe torsion quantity at this time is denoted by Δθ, the tip F of theline of sight vector is rotated by k4·Δθ (in radian).

As described above, the position of the viewing point E is movedaccording to the operation of the joystick 100A except the torsion(twisting) quantity exerted on the joystick 100A.

When the joystick 100A receives the torsion quantity (twisted), the tipF of the line of sight vector is rotated. Thus, since both of theviewing point E and the tip F of the line of sight vector can be moved,a more flexible scrolling can be achieved.

Although in the eighth embodiment the tip F of the line of sight vectoris rotated according to the torsion quantity acted upon the joystick100A, the viewing point E may be rotated according to the torsionquantity described above.

The same scrolling operation may be carried out in the same way as ineither case of the sixth or seventh embodiments when the joystick isoperated in the way except the torsion (twisting) of the joystick.

Although, in the fifth to eighth embodiments, the joystick 100A (100)which can be operated through an arbitrary angle is used, such anothertype of joystick as being capable of being operated only in apredetermined direction for example, a numeral 8 type direction.Alternatively, as shown in FIG. 28, a switch group 15 comprising aplurality of switches to instruct the scrolling direction and a switch16 to instruct a change in the scale of the reduction of the road mapmay be combined with the joystick in order to instruct the scrollingdirection.

Although, in the fifth to eighth embodiments, the scroll quantity isdetermined not only according to the operation direction of the joystickbut also according to the operating variables of the joystick, thedetection of the operating variables on the joystick may not be carriedout but only the operation direction of the joystick may be detected andinstructed, with the scroll quantity always constant.

Furthermore, the operation of the mode switch and a special operation ofthe joystick may permit the selection of one of the scrolling operationsdescribed in the fifth embodiment through the eighth embodiment.

As described hereinabove, since the vehicular navigating apparatus andmethods according to the present invention, the bird's eye view of theroad map is displayed on the display image screen of the display unitsuch that the viewing point is set on the upper sky located in thedirection opposite to the set destination with the present position ofthe vehicle as the reference and the road map surrounding the presentposition of the vehicle is viewed from the viewing point, the part ofthe road map surrounding the present position of the vehicle is extendedand the set optimum route of travel is displayed up to a location nearthe set destination in the continuous reduction scale image pattern.Hence, it is not necessary to provide a switch to change the reductionscale percentage and display range of the road map is not limited.

The invention should be understood to include all possible embodimentsand modification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. An apparatus for navigating a vehicle using adisplay unit, comprising:a) road map storing means for storing a roadmap data related to a road map, the road map data including road networkimage data and character data related to the road map; b) vehicleposition detecting means for detecting a present position of thevehicle; c) vehicle destination setting means through which adestination the vehicle is desired to reach is set on the road map; d)start point setting means for setting a start point of location on theroad map at which the vehicle is to start on the basis of the detectedposition of the vehicle; e) route of travel setting means for setting aroute of travel on the road map from the start point to the setdestination; and f) display control means for controlling an image ofthe road map surrounding the set route of travel which is displayed onthe display unit in a form of a bird's eye view such that the bird's eyeas a viewing point is referenced at a predetermined position on a raisedplane from said road map and offset in a direction opposite to the setdestination with respect to the present position of the vehicle beingdisplayed to appear to a user as looking down over the road map from thebird's eye, said road network image data being displayed on the displayunit in a perspective view from the bird's eye view image of the roadmap and the character data being displayed on the display unit as planedata at a constant size regardless of a position of the displayed imagescreen on the display unit with respect to the present position of thevehicle.
 2. An apparatus for navigating a vehicle using a display unitas claimed in claim 1, which further comprises:g) first road networkimage data extracting means for extracting a first part of the roadnetwork image data to be displayed on a first part of the image data tobe displayed on a second part of the display image screen of the displayunit, the first part of the display image screen corresponding to adisplay area from a lowest side of the display image screen up to apredetermined height thereof as viewed externally from the display unit;h) second road network image data for extracting a second part of theroad network display image screen of the display unit, the second partof the display image screen corresponding to another display area fromthe predetermined height up to a highest side of the display imagescreen as viewed externally from the display unit; and i) firstcharacter data extracting means for extracting a first part of thestored character data to be displayed on the first part of the displayimage screen; and j) second character data extracting means forextracting a second part of the stored character data to be displayed onthe second part of the display image screen, and wherein said displayimage control means controls the image to be displayed on the displayimage screen of the display unit in the form of the bird's eye view suchthat the first part of the road network image data extracting means isdisplayed onto the second part of the road network image data on thefirst part of the character data on the first part of the display imagescreen after the first part of the character data extracted by the firstcharacter data extracting means has been displayed on the first part ofthe display image screen, and the second part of the stored characterdata extracted by the second character data extracting means is, inturn, displayed onto the second part of the display image screen afterthe second part of the stored road network data extracted by the secondroad network data extracting means has been displayed on the second partof the display image screen.
 3. The apparatus of claim 1, furthercomprising:g) first road network image data extracting means forextracting a first part of the road network image data to be displayedon a first part of the display image screen of the display unit, thefirst part of the display image screen corresponding to a display areafrom a lowest side of the display image screen up to a predeterminedheight thereof as viewed externally from the display unit; h) secondroad network image data extracting means for extracting a second part ofthe road network display image screen of the display unit, the secondpart of the display image screen corresponding to another display areafrom the predetermined height up to a highest side of the display imagescreen as viewed externally from the display unit; and i) firstcharacter data extracting means for extracting a first part of thestored character data to be displayed on the first part of the displayimage screen; and j) second character data extracting means forextracting a second part of the stored character data to be displayed onthe second part of the display image screen, and wherein said displayimage control means controls the image to be displayed on the displayimage screen of the display unit in the form of the bird's eye view suchthat the first part of the road network image data extracted by thefirst road network image data extracting means is displayed onto thefirst part of the character data on the first part of the display imagescreen after the first part of the character data extracted by the firstcharacter data extracting means has been displayed on the first part ofthe display image screen, and the second part of the stored characterdata extracted by the second character data extracting means is, inturn, displayed onto the second part of the display image screen afterthe second part of the stored road network data extracted by the secondroad network data extracting means has been displayed on the second partof the display image screen; wherein the first part of the display imagescreen corresponds to a part of the road map ranging from the presentposition of the vehicle to a predetermined distance away from the setdestination and the second part of the display image screen correspondsto the remaining part of the road map ranging from the predetermineddistance to the set destination and wherein said character data includesnames of places.
 4. The apparatus of claim 1, wherein said road mapstoring means stores the road map including road network image data andcharacter data related to the road map, which further comprises:g) firstroad network image data extracting means for extracting a first part ofthe road network image data to be displayed on a first part of thedisplay image screen of the display unit, the first part of the displayimage screen corresponding to a first range of the road map within whicha part of the road network ranging from the present position of thevehicle to a predetermined distance away from the set destination; h)second road network image data extracting means for extracting a secondpart of the road network image data to be displayed on a second part ofthe display image screen of the display unit, the second part of thedisplay image screen corresponding to a second range of the road mapwithin which the remaining part of the road network ranging from thepredetermined distance to the set destination falls; i) first characterdata extracting means for extracting a first part of the storedcharacter data to be displayed on the first part of the display imagescreen of the display unit; and j) second character data extractingmeans for extracting a second part of the stored character data to bedisplayed on the second part of the display image screen of the displayunit, and wherein said display image control means controls the image tobe displayed on the display image screen in the form of the bird's eyeview such that the first part of the road network image data extractedby the first road network image data extracting means is displayed ontothe first part of the character data on the first part of the displayimage screen, the first part thereof corresponding to a predetermineddisplay area from a lowest side of the display image screen to apredetermined height thereof as viewed externally from the display unit,after said first part of the stored character data extracted by thefirst character data extracting means has been displayed on the firstpart of the display image screen of the display unit, and the secondpart of the stored character data extracted by the second character dataextracting means is displayed onto the second part of the road networkdata on the second part of the display image screen, the second part ofthe display image screen corresponding to the remaining display areafrom a highest side of the display image screen to the predeterminedheight as viewed externally from the display unit, after the second partof the stored road network data extracted by the second road networkdata extracting means has been displayed on the second part of thedisplay image screen of the display unit; k) bird's eye view generatingmeans for generating a plurality of bird's eye views each achieved whenthe bird's eye as a viewing point is placed on an upper sky offset inthe direction opposite to the set destination with the present positionof the vehicle as the reference and the road map surrounding the setroute of travel is being looked down over from the viewing point andeach bird's eye view having either of a different line of sight towardthe set destination or a different height from the earth; and l) bird'seye view selecting means for selecting one of the bird's eye views whichis to be displayed on the display image screen by said display imagecontrol means according to on which the bird's eye view a longestdistance of the set route of travel is to be displayed.
 5. The apparatusof claim 1, further comprising:g) first road network image dataextracting means for extracting a first part of the road network imagedata to be displayed on a first part of the display image screen of thedisplay unit, the first part of the display image screen correspondingto a display area from a lowest side of the display image screen up to apredetermined height thereof as viewed externally from the display unit;h) second road network image data extracting means for extracting asecond part of the road network image data to be displayed on a secondPart of the display image screen of the display unit, the second part ofthe display image screen corresponding to another display area from thepredetermined height up to a highest side of the display image screen asviewed externally from the display unit; and i) first character dataextracting means for extracting a first part of the stored characterdata to be displayed on the first part of the display image screen; andj) second character data extracting means for extracting a second partof the stored character data to be displayed on the second part of thedisplay image screen of the display unit, and wherein said display imagecontrol means controls the image to be displayed on the display imagescreen in the form of the bird's eye view such that the first part ofthe road network image data extracted by the first road network imagedata extracting means is displayed onto the first part of the characterdata on the first part of the display image screen, after said firstpart of the stored character data extracted by the first character dataextracting means has been displayed on the first part of the displayimage screen of the display unit, and the second part of the storedcharacter data extracted by the second character data extracting meansis displayed onto the second part of the road network image data onafter the second part of the stored road network image data extracted bythe second road network image data extracting means has been displayedon the second part of the display image screen of the display unit; inwhich the first part of the display image screen corresponds to a partof the road map ranging from the present position of the vehicle to apredetermined distance away from the set destination and the second partof the display image screen corresponds to the remaining part of theroad map ranging from the predetermined distance to the set destinationand wherein said character data include names of places; and furthercomprising k) bird's eye view generating means for generating aplurality of bird's eye views each achieved when the bird's eye as aviewing point is placed on an upper sky offset in the direction oppositeto the set destination with the present position of the vehicle as thereference and the road map surrounding the set route of travel is beinglooked down over from the viewing point and each bird's eye view havingeither of a different line of sight toward the set destination or adifferent height from the earth; and l) bird's eye view selecting meansfor selecting one of the bird's eye views which is to be displayed onthe display image screen by said display image control means accordingto on which the bird's eye view a longest distance of the set route oftravel is to be displayed; wherein said bird's eye view selecting meansselects one of the respective bird's eye views as being one of the linesof sight in the direction through which the sum of the length of eachroute link between nodes on the set route of travel displayed on therespective bird's eve view is a maximum; and wherein the display unit isa full color display unit, and wherein said display image control meanscontrols the image to be displayed on the display image screen in theform of the desired bird's eye view such that the roads transformed intothe bird's eye view are displayed on the display image screen indifferent display colors according to ranks of roads on the road map. 6.The apparatus of claim 1, wherein said road map storing means stores theroad map including road network image data and character data related tothe road map, which further comprises:g) first road network image dataextracting means for extracting a first part of the road network imagedata to be displayed on a first part of the display image screen of thedisplay unit, the first part of the display image screen correspondingto a first range of the road map within which a part of the road networkranging from the present position of the vehicle to a predetermineddistance away from the set destination; h) second road network imagedata extracting means for extracting a second part of the road networkimage data to be displayed on a second part of the display image screenof the display unit, the second part of the display image screencorresponding to a second range of the road map within which theremaining part of the road network ranging from the predetermineddistance to the set destination falls; i) first character dataextracting means for extracting a first part of the stored characterdata to be displayed on the first part of the display image screen ofthe display unit; and j) second character data extracting means forextracting a second part of the stored character data to be displayed onthe second part of the display image screen of the display unit, andwherein said display image control means controls the image to bedisplayed on the display image screen in the form of the bird's eye viewsuch that the first part of the road network image data extracted by thefirst road network image data extracting means is displayed onto thefirst part of the character data on the first part of the display imagescreen, the first part thereof corresponding to a predetermined displayarea from a lowest side of the display image screen to a predeterminedheight thereof as viewed externally from the display unit, after saidfirst part of the stored character data extracted by the first characterdata extracting means has been displayed on the first part of thedisplay image screen of the display unit, and the second part of thestored character data extracted by the second character data extractingmeans is displayed onto the second part of the road network data on thesecond part of the display image screen, the second part of the displayimage screen corresponding to the remaining display area from a highestside of the display image screen to the predetermined height as viewedexternally from the display unit, after the second part of the storedroad network data extracted by the second road network data extractingmeans has been displayed on the second part of the display image screenof the display unit.
 7. The apparatus of claim 6, further comprising:k)bird's eye view generating means for generating a plurality of bird'seye views each achieved when the bird's eye as a viewing point is placedon an upper sky located in the direction opposite to the set destinationwith the present position of the vehicle as the reference and the roadmap surrounding the set route of travel is being looked down over fromthe viewing point and each bird's eye view having either of a differentline of sight toward the set destination or a different height of theearth; and l) bird's eye view selecting means for selecting one of theprepared bird's eye views which is to be displayed on the display imagescreen by said display image control means according to on which thebird's eye view a longest distance of the set route of travel is to bedisplayed; wherein said bird's eye view selecting means derives a totalvalue (Lθ), equal to the sum of the length of each route link betweennodes on the set route of travel displayed on the respective bird's eyeview, for each different line of sight and said bird's eye viewselecting means selects one of the respective bird's eye views as beingone of the lines of sight in the direction through which the total value(Lθ) is the maximum.
 8. The apparatus of claim 7,wherein the displayunit is a full color display unit, and wherein said display imagecontrol means controls the image to be displayed on the display imagescreen in the form of the desired bird's eye view such that the roadstransformed into the bird's eye view are displayed on the display imagescreen in different display colors according to ranks of roads on theroad map; and which further comprises: m) grid line painting means forpainting grid lines having any one of the same class of colors as thatto which the display color of at least one rank of the roads on the roadmap to be displayed on the display image screen of the display unit inthe form of the bird's eye view belongs and for painting grid lines onthe road map so that each crossing point of the grid lines has any oneof the same class of colors as that to which the display color of atleast one rank of the roads belongs.
 9. The apparatus of claim 7,wherein the display unit is a full color display unit, and wherein saiddisplay image control means controls the image to be displayed on thedisplay image screen in the form of the desired bird's eye view suchthat the roads transformed into the bird's eye view are displayed on thedisplay image screen in different display colors according to ranks ofroads on the road map; and which further comprises:m) grid line paintingmeans for painting grid lines having any one of the same class of colorsas that to which the display color of at least one rank of the roads onthe road map to be displayed on the display image screen of the displayunit in the form of the bird's eye view belongs.
 10. The apparatus ofclaim 9, further comprising grid line painting means for painting gridlines on the road map so that each crossing point of the grid lines asany one of the same class of colors as that to which the display colorof at least one rank of the road belongs; and whereinsaid display imagecontrol means displays the roads in the bird's eye view according to apredetermined display priority order on each rank of the roads includingthe set route of travel, and said grid line painting means paints thegrid lines with any one of the same class of colors as that to which thedisplay order of one of the roads having a lowest priority order of thepredetermined display priority order belongs.
 11. An apparatus fornavigating a vehicle using a display unit, comprising:a) road mapstoring means for storing road map data related to a road map; b)vehicle position detecting means for detecting a present position of thevehicle; c) vehicle destination setting means through which adestination the vehicle is desired to reach is set on the road map; d)start point setting means for setting a starting point location on theroad map at which the vehicle is to start based on the detected presentposition of the vehicle; e) route of travel setting means for setting aroute of travel on the road map from the starting point to thedestination set; (f) display control means for controlling an image ofthe road map surrounding the route of travel set which is displayed onthe display unit in a form of a bird's eye view such that the bird's eyeas a viewing point is referenced at a predetermined position on a raisedplane from said road map and offset in a direction opposite to the setdestination with respect to the present position of the vehicle, and theroad map surrounding the set route of travel is being displayed toappear to a user as looking down over the road map from the bird's eye;and g) hairpin curve detecting means for detecting whether at least onehairpin curve is present in the set route of travel at a location whichis in a direction opposite to the set destination with respect to thepresent position of the vehicle as the reference, and informing saiddisplay control means of the presence of the hairpin curve when it isdetected, wherein said display control means, responsive to theinformation from the hairpin curve detecting means that the hairpincurve is present, controls the image of the set route of travel to bedisplayed on the display image screen of the display unit in the form ofthe bird's eye view so that the point of view of the bird's eye view ismoved from the predetermined position toward a direction opposite to thepresent position of the vehicle offset with respect to the detectedhairpin curve so that the road map surrounding the set route of travelis viewed including the detected hairpin curve.
 12. An apparatus fornavigating a vehicle using a display unit as claimed in claim 11, whichfurther comprises: h) position area determining means for determining aposition of a region and an area of the region, the region beingenclosed by a line segment orthogonal to another line segment connectingthe present position of the vehicle to the set destination and beingenclosed by the hairpin curve detected by said hairpin curve detectingmeans, and wherein said display control means controls the image of theroad map surrounding the set route of travel including a part of theroad map corresponding to the region in the form of the bird's eye view.13. An apparatus for navigating a vehicle using a display unit asclaimed in claim 11, wherein said hairpin curve detecting means includeshairpin curve length and direction determining means for determining alength and direction of the detected hairpin curve and wherein saiddisplay control means includes changing means for changing at leasteither of the predetermined position of the viewing point or a directionof a line of sight of the bird's eye view according to the determinedlength and direction of the detected hairpin curve.
 14. An apparatus fornavigating a vehicle using a display unit as claimed in claim 11,wherein said road map storing means stores the road map including roadnetwork image data and character data related to the road map, whichfurther comprises:g) first road network image data extracting means forextracting a first part of the road network image data to be displayedon a first part of the display image screen of the display unit, thefirst part of the display image screen corresponding to a first range ofthe road map within which a part of the road network ranging from thepresent position of the vehicle to a predetermined distance away fromthe set destination; h) second road network image data extracting meansfor extracting a second part of the road network image data to bedisplayed on a second part of the display image screen of the displayunit, the second part of the display image screen corresponding to asecond range of the road map within which the remaining part of the roadnetwork ranging from the predetermined distance to the set destinationfails; i) first character data extracting means for extracting a firstpart of the second character data to be displayed on the first part ofthe display image screen of the display unit; and j) second characterdata extracting means for extracting a second part of the storedcharacter data to be displayed on the second part of the display imagescreen of the display unit, and wherein said display image control meanscontrols the image to be displayed on the display image screen in thefor of the bird's eye view such that the first part of the road networkimage data extracted by the first road network image data extractingmeans is displayed onto the first Dart of the character data on thefirst part of the display image screen, the first part thereofcorresponding to a predetermined display area from a lowest side of thedisplay image screen to a predetermined height thereof as viewedexternally from the display unit, after said first part of the storedimage character data extracted by the first character data extractingmeans has been displayed on the first part of the display image screenof the display unit, and the second part of the stored character dataextracted by the second character data extracting means is displayedonto the second part of the road network data on the second part of thedisplay image screen, the second part of the display image screencorresponding to the remaining display area from a highest side of thedisplay image screen to the predetermined height as viewed externallyfrom the display unit, after the second part of the stored road networkdata extracted by the second road network data extracting means has beendisplayed on the second part of the display image screen of the displayunit.
 15. An apparatus for navigating a vehicle using a display unit asclaimed in claim 11, wherein said road map storing means stores the roadmap data including road network image data and character data related tothe road map, which further comprises:g) first road network image dataextracting means for extracting a first part of the road network imagedata to be displayed on a first part of the display image screen of thedisplay unit, the first part of the display image screen correspondingto a display area from a lowest side of the display image screen up to apredetermined height thereof as viewed externally from the display unit;h) second road network image data extracting means for extracting asecond part of the road network image data to be displayed on a secondpart of the display image screen of the display unit, the second part ofthe display image screen corresponding to another display area from thepredetermined height up to a highest side of the display image screen asviewed externally form the display unit; i) first character dataextracting means for extracting a first part of the stored characterdata to be displayed on the first part of the display image screen; andj) second character data extracting means for extracting a second partof the stored character data to be displayed on the second part of thedisplay image screen; and wherein said display image control meanscontrols the image to be displayed on the display image screen of thedisplay unit in the form of the bird's eye view such that the first partof the road network image data extracted by the first road network imagedata extracting means is displayed onto the first part of the characterdata on the first part of the display image screen after the first partof the character data extracted by the first character data extractingmeans has been displayed on the first part of the character dataextracted by the first character data extracting means has beendisplayed on the first part of the display image screen, and the secondpart of the stored character data extracted by the second character dataextracting means is, in turn, displayed onto the second part of the roadnetwork data on the second part of the display image screen after thesecond part of the stored road network data extracted by the second roadnetwork data extracting means has been displayed on the second part ofthe display image screen.
 16. An apparatus for navigating a vehicleusing a display unit as claimed in claim 15, wherein the first part ofthe display image screen corresponds to a part of the road map rangingfrom the present position of the vehicle to a predetermined distanceaway from the set destination and the second part of the display imagescreen corresponds to the remaining part of the road map ranging fromthe predetermined distance to the set destination and wherein saidcharacter data include names of places.
 17. An apparatus for navigatinga vehicle using a display unit as claimed in claim 11, which furthercomprises:g) bird's eye view generating means for generating a pluralityof bird's eye views each achieved when the bird's eye as a viewing pointis placed on an upper sky located in the direction opposite to the setdestination with the present position of the vehicle as the referenceand the road map surrounding the set route of travel is being lookeddown over from the viewing point and each bird's eye view having eitherof a different line of sight toward the set destination or a differentheight to the earth; and h) bird's eye view selecting means forselecting one of the prepared bird's eye views which is to be displayedon the display image screen by said display image control meansaccording to on which the bird's eye view a longest distance of the setroute of travel is to be displayed.
 18. An apparatus for navigating avehicle using a display unit as claimed in claim 17, wherein said bird'seye view generating means generates a plurality of bird's eye viewshaving a respectively different line of sight, said bird's eve viewselecting means derives a total value (Lθ), equal to the sum of thelength of each route link between nodes on the set route of traveldisplayed on the respective bird's eye view, for each different line ofsight and said bird's eye view selecting means selects one of therespective bird's eye views as being one of the lines of sight in thedirection through which the total value (Lθ) is a maximum.
 19. Anapparatus for navigating a vehicle using a display unit as claimed inclaim 11, wherein the display unit is a full color display unit, andwherein said display image control means controls the image to bedisplayed on the display image screen in the form of the desired bird'seye view such that the roads transformed into the bird's eye view aredisplayed on the display image screen in different display colorsaccording to ranks of roads on the road map.
 20. An apparatus fornavigating a vehicle using a display unit as claimed in claim 19, whichfurther comprises:g) grid line painting means for painting grid lineshaving any one of the same class of colors as that to which the displaycolor of at least one rank of the roads on the road map to be displayedon the display image screen of the display unit in the form of thebird's eye view belongs.
 21. An apparatus for navigating a vehicle usinga display unit as claimed in claim 20, wherein said display imagecontrol means displays the roads in the bird's eye view according to apredetermined display priority order on each rank of the roads includingthe set route of travel and said grid line painting means paints thegrid lines with any one of the same class of colors as that to which thedisplay of one of the roads having a lowest priority order of thepredetermined display priority order belongs.
 22. An apparatus fornavigating a vehicle using a display unit as claimed in claim 19, whichfurther comprises:g) grid line painting means for painting grid lines onthe road map so that each crossing point of the grid lines has any oneof the same class of colors as that to which the display color of atleast one rank of the roads belongs.
 23. An apparatus for navigating avehicle using a display unit as claimed in claim 22, wherein saiddisplay image control means displays the roads in the bird's eye viewaccording to a predetermined display priority order on each rank of theroads including the set route of travel, and said grid line paintingmeans paints the grid lines with any one of the same class of colors asthat to which the display order of one of the roads having a lowestpriority order of the predetermined display priority order belongs. 24.An apparatus for navigating a vehicle using a display unit as claimed inclaim 19, which further comprise: g) background painting means forpainting a background of the road map in any one of the same class ofcolors as that to which the display color of at least one rank of theroads belongs.
 25. An apparatus for navigating a vehicle using a displayunit as claimed in claim 24, wherein said display image control meansdisplays the roads according to a predetermined display priority orderfor each rank of the roads, and said background painting means paintsthe background in any one of the classes of colors as that to which thedisplay order of one of the roads having a lowest priority order foreach rank of the roads belongs.
 26. An apparatus for navigating avehicle using a display unit as claimed in claim 19, which furthercomprises: g) background painting means for painting a background of theroad map displayed on the display image screen by changing the displaycolors incrementally in a stepwise manner as the part of the road mapimage displayed becomes nearer to the destination so that a backgroundcolor of a part of the road map which is remote from the presentposition of the vehicle belongs to the same class of colors as thedisplay color to which at least one rank of the roads belongs.
 27. Anapparatus for navigating a vehicle using a display unit as claimed inclaim 26, wherein said display image control means displays the roadsaccording to a predetermined display priority order for each rank of theroads, and said background painting means paints the background with anyone of the same class of colors as that to which the display of thepredetermined display priority order for each rank of the roads belongs.28. An apparatus for navigating a vehicle using a display unit asclaimed in claim 19, which further comprises: g) dots painting means forpainting a plurality of background dots having at least one of the sameclasses of colors as those to which the display color of at least onerank of the roads belongs so that the dots which are present on a partof the road map, the part surrounding the present position of thevehicle, becomes coarse and those on another part of the road map whichis remote from the present position of the vehicle becomes fine.
 29. Anapparatus for navigating a vehicle using a display unit as claimed inclaim 26, wherein said display image control means displays the roadsaccording to a predetermined display priority order for each rank of theroads, and said dots painting means paints the dots in any one of thesame classes of colors as those to which the display order of one of theroads having a lowest priority order of the predetermined displaypriority order for each rank of the roads belongs.
 30. An apparatus fornavigating a vehicle using a display unit as claimed in claim 29,wherein the predetermined display priority order is the order offreeways, national highways, regional principle roads, principle roads,and street roads.
 31. A method for navigating a vehicle using a displayunit, comprising the steps of:a) storing a road map data related to aroad map in a predetermined storing means; b) detecting a presentposition of the vehicle; c) setting a destination the vehicle is desiredto reach on the road map; d) setting a start point of location on theroad map at which the vehicle is to start on the basis of the detectedpresent position of the vehicle; e) setting a route of travel on theroad map from the start point to the destination set; and f) displayingon a display image screen of the display unit the image of the road mapsurrounding the set route of travel; and g) operatively transforming acoordinate system of the road map surrounding the set route of travelinto a form of a bird's eye view such that the bird's eye as a viewingpoint is referenced at a predetermined position on a raised plane fromsaid road map and offset in a direction opposite to the set destinationwith respect to the present position of the vehicle, and the road mapsurrounding the set route of travel being displayed to appear to a useras looking down over the road map from the bird's eye; h) detectingwhether at least one hairpin curve is present preceding the currentposition in the set route of travel at a location which is in adirection opposite to the set destination with respect to the presentposition of the vehicle as the reference; and wherein, at said step g),the image of the set route of travel to be displayed on the displayimage screen of the display unit is controlled in the form of the bird'seye view so that the viewing point of the bird's eye view is moved fromthe predetermined position toward a direction opposite to the presentposition of the vehicle with respect to the detected hairpin curve sothat the road map surrounding the set route of travel is viewedincluding the detected hairpin curve.
 32. A method for navigating avehicle using a display unit, comprising the steps of:a) storing a roadmap data related to a road map, the road map data including road networkimage data and character data related to the road map; b) detecting apresent position of the vehicle; c) setting a destination of the vehicleis desired to reach is set on the road map; d) setting a start point oflocation on the road map at which the vehicle is to start on the basisof the detected present position of the vehicle; e) setting a route oftravel on the road map from the start point to the set destination; andf) displaying on a display image screen of the display unit the image ofthe road map and the character data surrounding the set route of travel;and g) operatively transforming a coordinate system of only the road mapimage data surrounding the set route of travel into a form of a bird'seye view such that the bird's eye as a viewing point is referenced at apredetermined position on a raised plane from said road map and offsetin a direction opposite to the set destination with respect to thepresent position of the vehicle, and the road map image data onlysurrounding the set route of travel being displayed in a perspectiveview to appear to a user as looking down over the road map from thebird's eye and the character data being displayed as plane data withoutthe coordinate transformation to the bird's eye view and being displayedat a constant size regardless of a position of the display image screenwith respect to the present position of the vehicle.
 33. An apparatusfor navigating a vehicle using a display unit, comprising:a) road mapstoring means for storing road map data related to a road map, the roadmap data including road network image data and character data related tothe road map; b) vehicle position detecting means for detecting apresent position of the vehicle; c) vehicle destination setting meansthrough which a destination the vehicle is desired to reach is set onthe road map; d) start point setting means for setting a starting pointlocation on the road map at which the vehicle is to start based on thedetected present position of the vehicle; e) route of travel settingmeans for setting a route of travel on the road map from the startingpoint to the destination set; and f) display control means forcontrolling an image of the road map surrounding the route of travel setwhich is displayed on the display unit in a form of a bird's eye viewsuch that the bird's eye as a viewing point is referenced at apredetermined position on a raised plane from said road map and offsetin a direction opposite to the set destination with respect to thepresent position of the vehicle, and the road map surrounding the setroute of travel is being displayed to appear to a user as looking downover the road map from the bird's eye, said character data beingoverwritten on the road network data displayed on the display unit inthe bird's eye view, the superposition of the character data on the roadmap or the superposition of the road map on the character data beingchanged depending on a height position of the road map image on an imagescreen of the display unit with respect to a lowest position of thedisplay unit.